Thyroid Hormones and Methylmercury Toxicity

Abstract

Thyroid hormones are essential for cellular metabolism, growth, and development. In particular, an adequate supply of thyroid hormones is critical for fetal neurodevelopment. Thyroid hormone tissue activation and inactivation in brain, liver, and other tissues is controlled by the deiodinases through the removal of iodine atoms. Selenium, an essential element critical for deiodinase activity, is sensitive to mercury and, therefore, when its availability is reduced, brain development might be altered. This review addresses the possibility that high exposures to the organometal, methylmercury (MeHg), may perturb neurodevelopmental processes by selectively affecting thyroid hormone homeostasis and function.

Environmentally Induced Oxidative Stress and Disruption of Brain Thyroid Hormone Homeostasis in Autism Spectrum Disorders

“…Thus, environmental contaminants that sequester selenium or induce oxidative stress are likely to affect deiodinase activity. Met-Hg has been shown to interact with selenium (Soldin et al, 2008) and can inhibit the function of selenoproteins such as the deiodinases (Watanabe et al, 2001). We have also shown that TM exposure increases levels of oxidative stress (Sulkowski et al, accepted), which has been found previously to decrease expression of the Dio2 gene (Lamirannd et al, 2008).…”

Biomarkers of chronic fluoride exposure in groundwater in a highly exposed population

“…NRC, 2006) review report also raised several other potential health concerns related to high F − exposure including altered biochemical and physiological processes, cardiovascular, reproductive, endocrine, gastrointestinal, neurological consequences, and bone fractures. Furthermore, excessive F − exposure is emerging as a potential neurotoxic agent in that it has been linked to lower intelligence quotient (IQ) in children (Grandjean et al, 2014; Choi et al, 2012; Tang et al, 2008). The research on these various potential health effects is fairly new and the findings require validation through well-designed and well-conducted population-based studies to better understand these potential effects of F − on human health.…”

Multiple metals predict prolactin and thyrotropin (TSH) levels in men

“…TSH stimulates secretion of thyroid hormones, which are vital to a number of physiological processes including metabolism, reproduction, and neurodevelopment. There is limited evidence that a number of metals may affect thyroid function, including inorganic arsenic (Davey et al 2008), cadmium (Iijima et al 2007), lead (Dundar et al 2006), manganese (Soldin and Aschner 2007) and organic mercury (Soldin et al 2008), as well as copper, selenium and zinc (Arthur and Beckett 1999). Alterations in circulating thyroid hormone or TSH levels in relation to exposure may be due to effects at different levels of the hypothalamus-pituitary-thyroid axis, and/or may be a result of altered thyroid hormone transport and peripheral metabolism/deactivation (Zoeller et al 2007; Boas et al 2006).…”